1. Field of the Invention
This invention relates to a feedback control technique and, more particularly, to such technique for controlling an apparatus having multi-degrees of freedom.
2. Description of the Prior Art
Typically, multi-body mechanical devices, such as robotic manipulators or cranes, weapon pointing systems, articulated structures, and the like, have nonlinear dynamics associated therewith. In these devices, the natural frequencies (that is, the structural modes of vibration) are dependent on the configuration of the respective device due to nonlinearities in the dynamics. In other words, as the device moves from one configuration (position) to another, the frequencies change. Another complication in controller synthesis for multi-body flexible devices is due to their input/state map not being feedback linearizable.
Typically, in such devices, proportional-derivative (PD) or proportional-integral-derivative (PID) controls are utilized for the rigid body motion and thereafter an outer loop controller is added to suppress the structural vibrations. The outer loop controller is normally designed to account for the large range of frequency variation which may exist due to geometric configuration changes of the respective device and, may actually be designed for the worst case thereof.
Presently, the above-described systems for controlling flexible multi-body devices compromise performance in order to achieve desired stability over the entire range of operation. For example, such systems may compromise the speed of response or control bandwidth, positional accuracy and so forth. Further, such systems may utilize a relatively complicated algorithm. As a result, the processing time may be relatively long and additional hardware may be needed to perform such processing, thereby resulting in increased costs.
Thus, the prior art has failed to provide an apparatus for providing feedback control of a device having multi-degrees of freedom which has a relatively high performance level throughout the desired operational range and which may be fabricated at a relatively low cost.